Systems are known for converting an image, such as characters of a document, to electrical signals which can be stored in a memory for later recall or transmitted to a remote location over, for example, telephone communication or similar systems. Systems of this type have generally been referred to as line scanners. In one type of line scanner, the document is held stationary and a photodetector or detectors are scanned across each line of the document along with a localized light source. In another type of scanner, the photodetector and light source are held stationary and the document is moved. In both types of systems, as the document is scanned, the high optical density or dark portions of the document reflect less light from the light source into the detector than the low optical density or light portions. As a result, the high and low optical density portions can be contrasted by the photodetector for generating electrical signals representative of the character images of the document.
While systems of the type above have been generally successful in fulfilling their intended purposes and have found commercial acceptance, these systems have exhibited several deficiencies. For example, line scanner systems are rather complex. They require mechanical drive and servo systems to precisely control the movement of the photosensor and light source relative to the document being scanned to enable accurate data storage or transmission of the electrical signals for the ultimate faithful reproduction of the document. When a single detector and light source are used, these mechanical drives and servo systems must accurately control such relative movement both across the document and down the length of the document.
When a plurality of colinear detectors and light sources are employed to enable line-by-line scanning of a document, fiber optics are generally used to convey light to operative association with each detector. Hundreds of individual detectors and corresponding optical fibers are required for such operation. This not only adds to the complexity of the overall system, but in addition, introduces fiber optic coupling problems as well.
Prior art line scanners also require frequent or periodic servicing. This results due to their complexity and the incorporation of moving parts which are subject to wear.
In addition to the foregoing, prior art line scanners require a significant period of time to scan a document. This is due to the fact that the mechanical moving parts can only be driven at a speed which precludes damage to the moving parts and which ensures proper synchronization with a companion printer or data input storage. Scanners of the prior art are therefore extremely inconvenient to use when a document of many pages must be scanned.
Lastly, prior art scanners are bulky in terms of size and heavy. This is due to the rather heavy mechanical parts incorporated therein and most particularly the motor or motors utilized for driving the moving parts. Hence, prior art scanners do not lend themselves to portability and generally can only be used at a fixed location.